MDEV-28300: Add upgrade test from MariaDB version 10.7 to 10.8

Salsa-CI does not have upgrade test from 10.7 to 10.8. Add that
to make sure nothing gets broke during update.

debian/salsa-ci.yml

@@ -555,6 +555,46 @@ mysql-8.0 Focal to mariadb-10.8 upgrade:
     variables:
       - $CI_COMMIT_TAG != null && $SALSA_CI_ENABLE_PIPELINE_ON_TAGS !~ /^(1|yes|true)$/
 
+mariadb.org-10.7 to mariadb-10.8 upgrade:
+  stage: upgrade extras
+  needs:
+    - job: build
+  image: debian:${RELEASE}
+  artifacts:
+    when: always
+    name: "$CI_BUILD_NAME"
+    paths:
+      - ${WORKING_DIR}/debug
+  script:
+    - *test-prepare-container
+    - apt install -y curl
+    - curl -sS https://mariadb.org/mariadb_release_signing_key.asc -o /etc/apt/trusted.gpg.d/mariadb.asc
+    - echo "deb https://deb.mariadb.org/10.7/debian ${RELEASE} main" > /etc/apt/sources.list.d/mariadb.list
+    - apt-get update
+    # Package libmariadbclient-dev from mariadb.org conflicts with libmariadb-dev in Sid, so cannot use wildcard that would include it
+    # Enable this line when there is a way to install them only from the mariadb.org repo
+    # - apt-get install -y 'mariadb*' libmariadb3 'libmariadb-*' 'libmariadbd*'
+    - apt-get install -y mariadb-server-10.7
+    - *test-verify-initial
+    # Install MariaDB built in this commit
+    # Force downgrades so our version installs on top of upstream revision, e.g. 1:10.5.5-1 vs 1:10.5.5+mariadb~sid
+    - apt-get install -y --allow-downgrades ./*.deb
+    # Verify installation of MariaDB built in this commit
+    - dpkg -l | grep -iE 'maria|mysql|galera' || true # List installed
+    - mariadb --version # Client version
+    - service mariadb status # There is no init.d/mysql in MariaDB 10.8
+    - *test-verify-final
+  variables:
+    GIT_STRATEGY: none
+  except:
+    variables:
+      - $CI_COMMIT_TAG != null && $SALSA_CI_ENABLE_PIPELINE_ON_TAGS !~ /^(1|yes|true)$/
+  allow_failure: true
+  # Installation on Sid fails on missing liburing1 because upstream 10.8
+  # MariaDB.org buildbot has not run 'apt upgrade' for a long time.
+  # Remove this allow_failure once buildbot has built a new 10.8
+  # release using latest liburing-dev in Debian Sid.
+
 mariadb.org-10.6 to mariadb-10.8 upgrade:
   stage: upgrade extras
   needs: